KABUL, Afghanistan (AP) — Two suicide bombers blew themselves up at an Afghan police headquarters Saturday, killing 12 officers in an area along the Pakistan border that still sees heavy Taliban attacks even as NATO pours in more troops and resources.

The Taliban claimed responsibility for the attack in eastern Paktika province, which has long been a refuge for Islamist extremists from around the world. It is one of the most violent areas of Afghanistan, where NATO and Afghan forces fight daily against the Haqqani network, a Pakistan-based Taliban faction closely tied to al-Qaida.

The attackers, who were disguised in police uniforms, made it through three security gates, said Nawab Waziry, the head of Paktika's provincial council. One attacker detonated his explosives inside the police headquarters building, while the other blew himself up near the entrance about 20 minutes later.

"The site was covered with blood," Waziry told The Associated Press after visiting the scene. He said an intelligence report several weeks ago warned that suicide attackers wearing police uniforms would strike soon.

"Even with all this information, still police were not able to prevent this attack," he said.

The blasts killed at least 12 officers and wounded 16, said Gen. Daud Andarabi, spokesman for the regional police commander in southeastern Afghanistan. Meyawer Khan, chief of the criminal investigation department for Paktika province, confirmed the death toll.

A NATO service member also was killed in a bomb attack in eastern Afghanistan on Saturday, but it was unclear if there was any connection to the Paktika bombing because the military coalition did not give any further details.

Although NATO forces have poured troops into the southern provinces of Kandahar and Helmand and have been making progress in rolling back the Taliban, fighting has continued in the eastern provinces where the Haqqani network holds sway.

The area, about 92 miles (150 kilometers) south of Kabul, borders the Pakistani region of North Waziristan and has been the target of numerous drone strikes against the Taliban, al-Qaida and the forces of the Haqqani network.

Saturday's attacks come amid a series of setbacks in efforts to negotiate an end to the nine-year war. The ongoing violence and intransigence of Taliban militants has led Western officials to advocate more strongly this year for a negotiated solution that would allow insurgents to have some sort of role in the government.

But in an embarrassing turn of events, a man initially believed to be a high-ranking Taliban representative was exposed this week as an impostor.

Afghanistan's intelligence service issued a statement Saturday saying it had discovered the man posing as Mullah Akhtar Mohammad Mansour was a fake and blocked him from entering Afghanistan from Pakistan for a planned meeting with Afghan government officials.

"He was about to come to Afghanistan. Then during a meeting with the intelligence service near the border, it was made clear that he was not Mansour, so the intelligence service did not bring him in to Afghanistan for the negotiations," the statement said.

But several newspaper reports said the impostor met with Afghan and NATO officials three times — including once with President Hamid Karzai — before they discovered he was not Mansour. He was allegedly paid to attend.

Karzai's office, however, has insisted the president never met with a man named Mullah Akhtar Mohammad Mansour.

The Afghan intelligence agency did confirm talks of some sort with the Taliban leadership, saying "there have been several contacts and negotiations in the several circles in the leadership of the Taliban and they are ongoing."

There also is tension stemming from the September parliamentary election, which was plagued by irregularities and voter intimidation. Election officials discarded 1.3 million ballots — nearly a quarter of the total — for fraud and disqualified 19 winning candidates for cheating.

Also Saturday, NATO said Afghan and coalition forces killed at least 15 insurgents during an overnight search for a senior Taliban leader in remote eastern Afghanistan. Security forces came under attack near a compound in Sherzad district of Nangarhar province on Friday night, sparking a battle that killed the insurgents.

Authorities were trying to determine whether the Taliban leader the troops were searching for was among those killed. The leader was not identified, but NATO said he helped foreign fighters, raised money and planned attacks against Afghan and coalition forces.